This paper draws on the extensive current literature in the field to provide a general guide and starting point for further study by presenting a short overview of the elements that contribute to endurance and how these can be trained in athletes. The full version of the paper can be downloaded using the button below.

The Physical Factors that Influence Endurance

Cardiovascular Factors

Cardiac Output: The volume of blood pumped by the heart per minute.
Stroke Volume: The amount of blood pumped by the heart with each contraction of the left ventricle.
Blood Flow to the Muscles: How quickly and efficiently oxygenated blood is transported to the muscles.

Muscular Factors

Once oxygen is delivered to the muscles, they have to use it to regenerate energy (ATP) for muscle contraction. The amount of oxygen extracted and used by the muscles is largely dependent on the muscles’ mitochondrial and capillary volumes.

Metabolic Factors

Lactate Removal: At high running velocities, there is an increased reliance on anaerobic glycolysis for the production of ATP, as the aerobic metabolism (Krebs cycle and electron transport chain) cannot keep up with the production of pyruvate from glycolysis. The pyruvate, therefore, is converted into lactate and lactate removal starts lagging behind lactate production, causing lactate to accumulate.

Buffering of Acidosis: The accumulation of hydrogen ions in muscles and blood, causing metabolic acidosis and the development of fatigue.

Carbohydrates Stored in Skeletal Muscle: Fatigue coincides with depletion of glycogen stored in skeletal muscle.

Neuromuscular Factors

The Neuromuscular Process: The central nervous system sends a signal to a motor neuron, which integrates with a number of muscle fibres, creating a motor unit. When this signal reaches the end of the axon of the motor neuron, the neurotransmitter acetylcholine is released at the neuromuscular junction. This causes a change in the polarity of the muscle membrane (called depolarisation), as sodium ions rush in and potassium ions rush out. The signal, now called an action potential, propagates deep into the muscle to the sarcoplasmic reticulum, which stores calcium ions. The calcium diffuses from the sarcoplasmic reticulum into the area of the contractile proteins—actin and myosin—and binds to a protein called troponin, which integrates with actin. Upon calcium binding to troponin, another protein called tropomyosin is removed from the active binding sites on the actin, exposing those sites to myosin. Myosin then binds to the actin, forming a cross-bridge. Finally, an ATP molecule contained inside the myosin is broken down into its constituents, releasing the energy contained within that molecule, allowing the muscle to contract.

During endurance running, for force production to continue, and for runners to maintain their pace, the central nervous system has to increase the number of motor units recruited and increase the frequency of stimulation of the motor units.

Methods for Improving Endurance Performance

Improving Cardiovascular Factors

Long interval training (3-5 minutes) performed at the velocity at which VO2 max occurs.

Example Sessions

• 5 x 1000m at vVO2max* with 1:<1 work-to-rest ratio

• 4 x 1200m at vVO2max* with 1:<1 work-to-rest ratio

• 16 x 400m at vVO2max with 1:<1 work-to-rest ratio

  *the velocity at which VO2max occurs

Improving Muscular Factors

High mileage with progressive increases in volume (days per week and duration) over time.

Example Session

• 30km at long run pace.

Improving Metabolic Factors

Lactate threshold training, performed as a continious workout or interval training.

Example Sessions

• 5-10km at lactuate threshold pace*

• 5-7 x 1500m at lactate threshold pace* with 1 minute rest between reps.

• Long runs of 15-25km
  * ‘Comfortably Hard’ or 80-90% max HR

Improving Neuromuscular Factors

Explosive, plyometrics, and heavy weights strength training.

Example Sessions

• Free weights (e.g. back squat, deadlifts, front squats) 3 or 4 sets of 3-5 reps at 85-90% of 1RM with 3 minutes rest.

• Plyometrics (e.g. box jumps, squat jumps, leg bounds, bleacher hops)